RGsB

RGsB (RGB with Sync on Green, also written SoG or Sync-on-Green) is an analog video signal format that transmits the red, green, and blue color channels on three 75Ω lines, with the synchronization (sync) information embedded within the green channel rather than carried on a separate wire. This reduces the connection to three conductors total, making RGsB the most cable-efficient of the RGB signal formats.

Overview

In RGsB, the composite sync signal (combined horizontal and vertical sync pulses) is added to the green channel during the blanking interval. The display must contain sync separation circuitry to extract the sync information from the green signal before processing it for display. Because the sync pulses ride below the black level of the green channel, they do not affect the visible image when properly handled.

RGsB is one of three common analog RGB sync configurations, differing in how synchronization is delivered:

Format	Wires	Sync method
RGBHV	5	Separate horizontal and vertical sync
RGBS	4	Composite sync on a dedicated wire
RGsB	3	Sync embedded in the green channel

The three-wire nature of RGsB means it uses the same number of conductors as YPbPr component video, and indeed shares the same physical connectors and cabling (three 75Ω cables with RCA or BNC connectors). This can cause confusion, as a device's three-cable "component" input might accept either YPbPr or RGsB depending on the equipment, and the two formats are not directly interchangeable without conversion.

Signal Characteristics

Parameter	Value
Signal type	Three-channel analog (R, G+sync, B)
R/B signal level	0.7V peak-to-peak, 75Ω impedance
G signal level	0.7V peak-to-peak video + 0.3V sync (below black level)
Sync type	Bi-level (SD) or tri-level (HD) composite sync on green
Impedance	75Ω per channel
Common connectors	BNC ×3 (professional), RCA ×3

For standard-definition signals, bi-level sync pulses are used, with the sync tip dropping approximately 0.3V below the black level on the green channel. For high-definition progressive signals (480p and above), tri-level sync is typically used, where the sync pulse dips below black level and then rises above it, providing a more precise timing reference.

Use on CRT Equipment

Sony Equipment

Sony has been the most prominent proponent of sync-on-green in the consumer and professional video space. Sony professional monitors, computer workstations, and the PlayStation line of game consoles all make use of RGsB in various contexts:

• Sony professional monitors — many Sony PVM and BVM monitors with BNC RGB inputs can auto-detect and accept RGsB alongside RGBS and RGBHV.
• Sony computer workstations — Silicon Graphics (SGI) workstations and some Sun Microsystems systems output RGsB natively, often through DB13W3 connectors. Sony's high-end Trinitron computer monitors (GDM series) support sync-on-green for compatibility with these systems.
• PlayStation 2 — the PS2 is the most commonly encountered consumer device that outputs RGsB. When set to progressive scan (480p) mode over its Multi AV output, the PS2 disables its composite video and luma sync outputs and switches to sync-on-green for its RGB signal. At 480i, the PS2 uses standard composite sync or sync-on-luma over its RGB output.

Multi-Sync Professional Monitors

Many multi-sync professional CRT monitors auto-detect sync type across their BNC inputs and can accept RGBHV, RGBS, or RGsB without manual configuration. This includes high-end models from Sony, Ikegami, Barco, and NEC. The monitor's sync processing circuitry detects whether sync is present on dedicated H/V lines, a separate composite sync line, or embedded in the green channel, and configures itself accordingly.

Computer Workstation Monitors

Before VGA's dominance, some Unix workstation environments (particularly SGI and Sun) standardized on RGsB because the three-wire approach simplified cabling in environments where long cable runs were common. The DB13W3 connector used by these systems carried three coaxial signals (R, G+sync, B) plus additional pins for identification. Monitors designed for these workstations natively support sync-on-green.

Compatibility Considerations

A display that does not support sync-on-green will exhibit distinct symptoms when fed an RGsB signal: typically a strong green tint across the entire image (because the sync pulses are interpreted as green video data) or no image at all (because the display cannot find sync on its expected sync input). This is a common issue when connecting workstation equipment to standard VGA monitors.

Conversely, feeding a standard RGBHV or RGBS signal to a display expecting RGsB will result in no sync lock, as the display looks for sync information in the green channel and finds none.

Conversion between RGsB and other RGB formats requires relatively simple circuitry:

• RGsB → RGBS: A sync stripper/separator IC extracts composite sync from the green channel and outputs it on a separate wire, while passing through clean green video.
• RGBHV → RGsB: A sync combiner first merges H and V sync into composite sync, then adds (sums) the composite sync onto the green channel.

Retro Gaming Relevance

For the retro gaming community, RGsB is primarily encountered in two contexts:

• PlayStation 2 progressive scan — when using RGB cables with a PS2 in 480p mode, the console outputs RGsB. Most SCART-equipped displays and many scalers (RetroTINK, OSSC) can handle this, though some equipment requires explicit RGsB/sync-on-green support. For this reason, many PS2 users prefer component video cables for progressive scan output, as component inputs are more universally supported.

• Workstation monitor reuse — CRT enthusiasts who acquire SGI or Sun workstation monitors will find they expect RGsB input. Adapters or sync combiners are needed to use these monitors with standard VGA or console RGB sources.

See Also

• RGBS — Four-wire RGB with composite sync
• RGBHV — Five-wire RGB with separate H and V sync
• VGA (RGBHV) — DE-15 connector carrying RGBHV
• Component (YPbPr) — Three-wire analog video using the same connectors but different signal encoding
• BNC — Professional connector commonly used for RGsB